Network Working Group J. Arkko
Internet-Draft Ericsson
Intended status: Informational T. Chown
Expires: May 3, 2012 University of Southampton
J. Weil
Time Warner Cable
O. Troan
Cisco Systems, Inc.
October 31, 2011
Home Networking Architecture for IPv6draft-chown-homenet-arch-01
Abstract
This text describes evolving networking technology within small
"residential home" networks. The goal of this memo is to define the
architecture for IPv6-based home networking and the associated
principles and considerations. The text highlights the impact of
IPv6 on home networking, illustrates topology scenarios, and shows
how standard IPv6 mechanisms and addressing can be employed in home
networking. The architecture describes the need for specific
protocol extensions for certain additional functionality. It is
assumed that the IPv6 home network runs as an IPv6-only or dual-stack
network, but there are no recommendations in this memo for the IPv4
part of the network.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 3, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
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Internet-Draft IPv6 Home Networking October 20111. Introduction
This memo focuses on evolving networking technology within small
"residential home" networks and the associated challenges. For
example, a trend in home networking is the proliferation of
networking technology in an increasingly broad range of devices and
media. This evolution in scale and diversity sets requirements on
IETF protocols. Some of these requirements relate to the need for
multiple subnets, for example for private and guest networks, the
introduction of IPv6, and the introduction of specialized networks
for home automation and sensors.
While advanced home networks have been built, most operate based on
IPv4, employ solutions that we would like to avoid such as (cascaded)
network address translation (NAT), or require expert assistance to
set up. The architectural constructs in this document are focused on
the problems to be solved when introducing IPv6 with a eye towards a
better result than what we have today with IPv4, as well as a better
result than if the IETF had not given this specific guidance.
This architecture document aims to provide the basis and guiding
principles for how standard IPv6 mechanisms and addressing [RFC2460]
[RFC4291] can be employed in home networking, while coexisting with
existing IPv4 mechanisms. In emerging dual-stack home networks it is
vital that introducing IPv6 does not adversely affect IPv4 operation.
Future deployments, or specific subnets within an otherwise dual-
stack home network, may be IPv6-only.
[RFC6204] defines basic requirements for customer edge routers
(CPEs). The scope of this text is the homenet, and thus the internal
facing interface described that RFC as well as other components
within the home network. While the network may be dual-stack or
IPv6-only, specific transition tools on the CPE are out of scope of
this text, as is any advice regarding architecture of the IPv4 part
of the network. We assume that IPv4 network architecture in home
networks is what it is, and can not be affected by new
recommendations.
2. Effects of IPv6 on Home Networking
Service providers are deploying IPv6, content is becoming available
on IPv6, and support for IPv6 is increasingly available in devices
and software used in the home. While IPv6 resembles IPv4 in many
ways, it changes address allocation principles, makes multi-
addressing the norm, and allows direct IP addressability and routing
to devices in the home from the Internet. This section presents an
overview of some of the key areas impacted by the implementation of
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IPv6 into the home network that are both promising and problematic:
Multiple segments and routers
Simple layer 3 topologies involving as few subnets as possible are
preferred in home networks for a variety of reasons including
simpler management and service discovery. However, the
incorporation of dedicated (routed) segments remains necessary for
a variety of reasons.
For instance, a common feature in modern home routers is the
ability to support both guest and private network segments. Also,
link layer networking technology is poised to become more
heterogeneous, as networks begin to employ both traditional
Ethernet technology and link layers designed for low-powered and
lossy networks (LLNs) such as those used for certain types of
sensor devices. Similar needs for segmentation may occur in other
cases, such as separating building control or corporate extensions
from the Internet access network. Also, different segments may be
associated with subnets that have different routing and security
policies.
Documents that provide some more specific background and depth on
this topic include: [I-D.herbst-v6ops-cpeenhancements],
[I-D.baker-fun-multi-router], and [I-D.baker-fun-routing-class].
In addition to routing, rather than NATing, between subnets, there
are issues of when and how to extend mechanisms such as service
discovery which currently rely on link-local addressing to limit
scope.
The presence of a multiple segment, multi-router network implies
that there is some kind of automatic routing mechanism in place.
In advanced configurations similar to those used in multihomed
corporate networks, there may also be a need to discover border
router(s) by an appropriate mechanism.
Multi-Addressing of devices
In an IPv6 network, devices may acquire multiple addresses,
typically at least a link-local address and a globally unique
address. Thus it should be considered the norm for devices on
IPv6 home networks to be multi-addressed, and to also have an IPv4
address where the network is dual-stack. Default address
selection mechanisms [I-D.ietf-6man-rfc3484-revise] allow a node
to select appropriate src/dst address pairs for communications,
though such selection may face problems in the event of
multihoming, where nodes will be configured with one address from
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each upstream ISP prefix, and the presence of upstream ingress
filtering thus requires multi-addressed nodes to select the right
source address to be used for the corresponding uplink.
Unique Local Addresses (ULAs)
[RFC4193] defines Unique Local Addresses (ULAs) for IPv6 that may
be used to address devices within the scope of a single site.
Support for ULAs for IPv6 CPEs is described in [RFC6204]. A home
network running IPv6 may deploy ULAs for communication between
devices within the network. ULAs have the potential to be used
for stable addressing in a home network where the externally
allocated global prefix changes over time or where external
connectivity is temporarily unavailable. However, it is
undesirable to aggressively deprecate global prefixes for
temporary loss of connectivity, so for this to matter there would
have to be a connection breakage longer than the lease period, and
even then, deprecating prefixes when there is no connectivity may
not be advisable. However, while setting a network up there may
be a period with no connectivity.
Another possible reason for using ULAs would be to provide an
indication to applications that the traffic is local. This could
then be used with security settings to designate where a
particular application is allowed to connect to.
Address selection mechanisms should ensure a ULA source address is
used to communicate with ULA destination addresses. The use of
ULAs does not imply IPv6 NAT, rather that external communications
should use a node's global IPv6 source address.
Security, Borders, and the elimination of NAT
Current IPv4 home networks typically receive a single global IPv4
address from their ISP and use NAT with private [RFC1918].
addressing for devices within the network. An IPv6 home network
removes the need to use NAT given the ISP offers a sufficiently
large IPv6 prefix to the homenet, allowing every device on every
link to be assigned a globally unique IPv6 address.
The end-to-end communication that is potentially enabled with IPv6
is both an incredible opportunity for innovation and simpler
network operation, but it is also a concern as it exposes nodes in
the internal networks to receipt of otherwise unwanted traffic
from the Internet.
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In IPv4 NAT networks, the NAT provides an implicit firewall
function. [RFC4864] suggests that IPv6 networks with global
addresses utilise "Simple Security" in border firewalls to
restrict incoming connections through a default deny policy.
Applications or hosts wanting to accept inbound connections then
need to signal that desire through a protocol such as uPNP or PCP
[I-D.ietf-pcp-base].
Such an approach would reduces the efficacy of end-to-end
connectivity that IPv6 has the potential to restore, since the
need for IPv4 NAT traversal is replaced by a need to use a
signalling protocol to request a firewall hole be opened.
[RFC6092] provides recommendations for an IPv6 firewall that
applies "limitations on end-to-end transparency where security
considerations are deemed important to promote local and Internet
security." The firewall operation is "simple" in that there is an
assumption that traffic which is to be blocked by default is
defined in the RFC and not expected to be updated by the user or
otherwise. The RFC does however state that CPEs should have an
option to be put into a "transparent mode" of operation.
It is important to distinguish between addressability and
reachability; i.e. IPv6 through use of globally unique addressing
in the home makes all devices potentially reachable from anywhere.
Whether they are or not should depend on firewall or filtering
configuration, and not the presence or use of NAT.
Advanced Security for IPv6 CPE [I-D.vyncke-advanced-ipv6-security]
takes the approach that in order to provide the greatest end-to-
end transparency as well as security, security polices must be
updated by a trusted party which can provide intrusion signatures
and other "active" information on security threats. This is much
like a virus-scanning tool which must receive updates in order to
detect and/or neutralize the latest attacks as they arrive. As
the name implies "advanced" security requires significantly more
resources and infrastructure (including a source for attack
signatures) in comparision to "simple" security.
In addition to establishing the security mechanisms themselves, it
is important to know where to enable them. If there is some
indication as to which router is connected to the "outside" of the
home network, this is feasible. Otherwise, it can be difficult to
know which security policies to apply where. Further, security
policies may be different for various address ranges if ULA
addressing is setup to only operate within the homenet itself and
not be routed to the Internet at large. Finally, such policies
must be able to be applied by typical home users, e.g. to give a
visitor in a "guest" network access to media services in the home.
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It may be useful to classify the border of the home network as a
unique logical interface separating the home network from service
provider network/s. This border interface may be a single
physical interface to a single service provider, multiple layer 2
sub-interfaces to a single service provider, or multiple
connections to a single or multiple providers. This border is
useful for describing edge operations and interface requirements
across multiple functional areas including security, routing,
service discovery, and router discovery.
Naming, and manual configuration of IP addresses
In IPv4, a single subnet NATed home network environment is
currently the norm. As a result, it is for example common
practice for users to be able to connect to a router for
configuration via a literal address such as 192.168.1.1 or some
other commonly used RFC 1918 address. In IPv6, while ULAs exist
and could potentially be used to address internally-reachable
services, little deployment experience exists to date. Given a
true ULA prefix is effectively a random 48-bit prefix, it is not
reasonable to expect users to manually enter such address literals
for configuration or other purposes. As such, even for the
simplest of functions, naming and the associated discovery of
services is imperative for an easy to administer homenet.
In a multi-subnet homenet, naming and service discovery should be
expected to operate across the scope of the entire home network,
and thus be able to cross subnet boundaries. It should be noted
that in IPv4, such services do not generally function across home
router NAT boundaries, so this is one area where there is scope
for an improvement in IPv6.
3. Architecture
An architecture outlines how to construct home networks involving
multiple routers and subnets. In this section, we present a set of
typical home network topology models/scenarios, followed by a list of
topics that may influence the architecture discussions, and a set of
architectural principles that govern how the various nodes should
work together. Finally, some guidelines are given for realizing the
architecture with the IPv6 addressing, prefix delegation, global and
ULA addresses, source address selection rules and other existing
components of the IPv6 architecture. The architecture also drives
what protocol extensions are necessary, as will be discussed in
Section 3.6.
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Internet-Draft IPv6 Home Networking October 20113.1. Network Models
Figure 1 shows the simplest possible home network topology, involving
just one router, a local area network, and a set of hosts. Setting
up such networks is in principle well understood today [RFC6204].
+-------+-------+ \
| Service | \
| Provider | | Service
| Router | | Provider
+-------+-------+ | network
| /
| Customer /
demarc #1 --> | Internet connection /
|
+------+--------+ \
| IPv6 | \
| Customer Edge | \
| Router | /
+------+--------+ /
| |
demarc #2 --> | | End-User
| Local network | network(s)
---+-----+-------+--- \
| | \
+----+-----+ +-----+----+ \
|IPv6 Host | |IPv6 Host | /
| | | | /
+----------+ +-----+----+ /
Figure 1
Two possible demarcation points are illustrated in Figure 1, which
indicate which party is responsible for configuration or
autoconfiguration. Demarcation #1 makes the Customer Edge Router the
responsibility of the customer. This is only practical if the
Customer Edge Router can function with factory defaults installed.
The Customer Edge Router may be pre-configured by the ISP, or by some
suitably simple method by the home customer. Demarcation #2 makes
the Customer Edge Router the responsibility of the provider. Both
models of operation must be supported in the homenet architecture,
including the scenarios below with multiple ISPs and demarcation
points.
Figure 2 shows another network that now introduces multiple local
area networks. These may be needed for reasons relating to different
link layer technologies in use or for policy reasons. Note that a
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common arrangement is to have different link types supported on the
same router, bridged together.
This topology is also relatively well understood today [RFC6204],
though it certainly presents additional demands with regards suitable
firewall policies and limits the operation of certain applications
and discovery mechanisms (which may typically today only succeed
within a single subnet).
+-------+-------+ \
| Service | \
| Provider | | Service
| Router | | Provider
+------+--------+ | network
| /
| Customer /
| Internet connection /
|
+------+--------+ \
| IPv6 | \
| Customer Edge | \
| Router | /
+----+-------+--+ /
Network A | | Network B | End-User
---+-------------+----+- --+--+-------------+--- | network(s)
| | | | \
+----+-----+ +-----+----+ +----+-----+ +-----+----+ \
|IPv6 Host | |IPv6 Host | | IPv6 Host| |IPv6 Host | /
| | | | | | | | /
+----------+ +-----+----+ +----------+ +----------+ /
Figure 2
Figure 3 shows a little bit more complex network with two routers and
eight devices connected to one ISP. This network is similar to the
one discussed in [I-D.ietf-v6ops-ipv6-cpe-router-bis]. The main
complication in this topology compared to the ones described earlier
is that there is no longer a single router that a priori understands
the entire topology. The topology itself may also be complex. It
may not be possible to assume a pure tree form, for instance. This
would be a consideration if there was an assumption that home users
may plug routers together to form arbitrary topologies.
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o Network security
3.3. Considerations
This section lists some considerations for home networking that may
affect the architecture and associated requirements.
Multihoming
A homenet may be multihomed to multiple providers. This may
either take a form where there are multiple isolated networks
within the home or a more integrated network where the
connectivity selection is dynamic. Current practice is typically
of the former kind, but the latter is expected to become more
commonplace.
In an integrated network, specific appliances or applications may
use their own external connectivity, or the entire network may
change its connectivity based on the status of the different
upstream connections. Many general solutions for IPv6 multihoming
have been worked on for years in the IETF, though to date there is
little deployment of these mechanisms. While an argument can be
made that home networking standards should not make another
attempt at this, the obvious counter-argument is that multihoming
support will be necessary for many deployment situations.
One such approach is the use of NPTv6 [RFC6296], which is a prefix
translation-based mechanism. An alternative is presented in
[I-D.v6ops-multihoming-without-ipv6nat]. Host-based methods such
as Shim6 [RFC5533] have also been defined.
In any case, if multihoming is supported additional requirements
are necessary. The general multihoming problem is broad, and
solutions may include complex architectures for monitoring
connectivity, traffic engineering, identifier-locator separation,
connection survivability across multihoming events, and so on.
However, there is a general agreement that for the home case, if
there is any support for multihoming it should be limited to a
very small subset of the overall problem. Specifically, multi-
addressed hosts selecting the right source address to avoid
falling foul of ingress filtering on upstream ISP connections
[I-D.baker-fun-multi-router]. A solution to this particular
problem is desirable.
Some similar multihoming issues have already been teased out in
the work described in [I-D.ietf-mif-dns-server-selection], which
has led to the definition of a DHCPv6 route option
[I-D.ietf-mif-dhcpv6-route-option].
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One could also argue that a "happy eyeballs" approach, not too
dissimilar to that proposed for multiple interface (mif)
scenarios, is also acceptable if such support becomes commonplace
in hosts and applications.
A further consideration and complexity here is that at least one
upstream may be a "walled garden", and thus only appropriate to be
used for connectivity to the services of that provider.
Quality of Service in multi-service home networks
Support for QoS in a multi-service homenet may be a requirement,
e.g. for a critical system (perhaps healthcare related), or for
differentiation between different types of traffic (file sharing,
cloud storage, live streaming, VoIP, etc). Different media types
may have different QoS properties or capabilities.
However, homenet scenarios should require no new QoS protocols. A
DiffServ [RFC2475] approach with a small number of predefined
traffic classes should generally be sufficient, though at present
there is little experience of QoS deployment in home networks.
There may also be complementary mechanisms that could be
beneficial in the homenet domain, such as ensuring proper
buffering algorithms are used as described in [Gettys11].
DNS services
A desirable target may be a fully functional self-configuring
secure local DNS service so that all devices are referred to by
name, and these FQDNs are resolved locally. This will make clean
use of ULAs and multiple ISP-provided prefixes much easier. The
local DNS service should be (by default) authoritative for the
local name space in both IPv4 and IPv6. A dual-stack residential
gateway should include a dual-stack DNS server.
Consideration will also need to be given for existing protocols
that may be used within a network, e.g. mDNS, and how these
interact with unicast-based DNS services.
With the introduction of new top level domains, there is potential
for ambiguity between for example a local host called apple and
(if it is registered) an apple gTLD, so some local name space is
probably required, which should also be configurable to something
else by a home user if desired.
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Privacy considerations
There are no specific privacy concerns for this text. It should
be noted that most ISPs are expected to offer static IPv6 prefixes
to customers, and thus the addresses they use would not generally
change over time.
3.4. Principles
There is little that the Internet standards community can do about
the physical topologies or the need for some networks to be separated
at the network layer for policy or link layer compatibility reasons.
However, there is a lot of flexibility in using IP addressing and
inter-networking mechanisms. In this section we provide some
guidance on how this flexibility should be used to provide the best
user experience and ensure that the network can evolve with new
applications in the future.
The following principles should be used as a guide in designing these
networks in the correct manner. There is no implied priority by the
order in which the principles are listed.
Reuse existing protocols
It is desirable to reuse existing protocols where possible, but at
the same time to avoid consciously precluding the introduction of
new or emerging protocols. For example,
[I-D.baker-fun-routing-class] suggests introducing a routing
protocol that may may route on both source and destination
addresses.
A generally conservative approach, giving weight to running code,
is preferable. Where new protocols are required, evidence of
commitment to implementation by appropriate vendors or development
communities is highly desirable. Protocols used should be
backwardly compatible.
Where possible, changes to hosts should be minimised. Some
changes may be unavoidable however, e.g. signalling protocols to
punch holes in firewalls where "Simple Security" is deployed in a
CPE.
Liaisons with other appropriate standards groups and related
organisations is desirable, e.g. the IEEE and Wi-Fi Alliance.
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Dual-stack Operation
The homenet architecture targets both IPv6-only and dual-stack
networks. While the CPE requirements in RFC 6204 are targeted at
IPv6-only networks, it is likely that dual-stack homenets will be
the norm for some period of time. IPv6-only networking may first
be deployed in home networks in "greenfield" scenarios, or perhaps
as one element of an otherwise dual-stack network. The homenet
architecture must operate in the absence of IPv4, and IPv6 must
work in the same scenarios as IPv4 today. Running IPv6-only may
require documentation of additional considerations such as:
Ensuring there is a way to access content in the IPv4 Internet.
This can be arranged through incorporating NAT64 [RFC6144]
functionality in the home gateway router, for instance.
DNS discovery mechanisms are enabled even for IPv6. Both
stateless DHCPv6 [RFC3736] [RFC3646] and Router Advertisement
options [RFC6106] may have to be supported and turned on by
default to ensure maximum compatibility with all types of hosts
in the network. This requires, however, that a working DNS
server is known and addressable via IPv6.
All nodes in the home network support operations in IPv6-only
mode. Some current devices work well with dual-stack but fail
to recognize connectivity when IPv4 DHCP fails, for instance.
In dual-stack networks, solutions for IPv6 must not adversely
affect IPv4 operation. It is likely that topologies of IPv4 and
IPv6 networks would be as congruent as possible.
Note that specific transition tools, particularly those running on
the border CPE, are out of scope. The homenet architecture
focuses on the internal home network.
Largest Possible Subnets
Today's IPv4 home networks generally have a single subnet, and
early dual-stack deployments have a single congruent IPv6 subnet,
possibly with some bridging functionality.
Future home networks are highly likely to need multiple subnets,
for the reasons described earlier. As part of the self-
organisation of the network, the network should subdivide itself
to the largest possible subnets that can be constructed within the
constraints of link layer mechanisms, bridging, physical
connectivity, and policy. For instance, separate subnetworks are
necessary where two different links cannot be bridged, or when a
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policy requires the separation of a private and visitor parts of
the network.
While it may be desirable to maximise the chance of link-local
protocols succeeding, multiple subnet home networks are
inevitable, so their support must be included. A general
recommendation is to follow the same topology for IPv6 as is used
for IPv4, but not to use NAT. Thus there should be routed IPv6
where an IPv4 NAT is used, and where there is no NAT there should
be bridging.
In some cases IPv4 NAT home networks may feature cascaded NATs,
e.g. where NAT routers are included within VMs or Internet
connection services are used. IPv6 routed versions of such tools
will be required.
Transparent End-to-End Communications
An IPv6-based home network architecture should naturally offer a
transparent end-to-end communications model. Each device should
be addressable by a unique address. Security perimeters can of
course restrict the end-to-end communications, but it is simpler
given the availability of globally unique addresses to block
certain nodes from communicating by use of an appropriate
filtering device than to configure the address translation device
to enable appropriate address/port forwarding in the presence of a
NAT.
As discussed previously, it is important to note the difference
between hosts being addressable and reachable. Thus filtering is
to be expected, while IPv6 NAT is not. End-to-end communications
are important for their robustness to failure of intermediate
systems, where in contrast NAT is dependent on state machines
which are not self-healing.
When configuring filters, protocols for securely associating
devices are desirable. In the presence of "Simple Security" the
use of signalling protocols such as uPnP or PCP may be expected to
punch holes in the firewall. Alternatively, RFC 6092 supports the
option for a border CPE to run in "transparent mode", in which
case a protocol like PCP is not required, but the security model
is more open.
IP Connectivity between All Nodes
A logical consequence of the end-to-end communications model is
that the network should by default attempt to provide IP-layer
connectivity between all internal parts as well as between the
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internal parts and the Internet. This connectivity should be
established at the link layer, if possible, and using routing at
the IP layer otherwise.
Local addressing (ULAs) may be used within the scope of a home
network. It would be expected that ULAs may be used alongside one
or more globally unique ISP-provided addresses/prefixes in a
homenet. ULAs may be used for all devices, not just those
intended to have internal connectivity only. ULAs may then be
used for stable internal communications should the ISP-provided
prefix change, or external connectivity be temporarily lost. The
use of ULAs should be restricted to the homenet scope through
filtering at the border(s) of the homenet; thus "end-to-end" for
ULAs is limited to the homenet.
In some cases full internal connectivity may not be desirable,
e.g. in certain utility networking scenarios, or where filtering
is required for policy reasons against guest network subnet(s).
Note that certain scenarios may require co-existence of ISP
connectivity providing a general Internet service with provider
connectivity to a private "walled garden" network.
Some home networking scenarios/models may involve isolated
subnet(s) with their own CPEs. In such cases connectivity would
only be expected within each isolated network (though traffic may
potentially pass between them via external providers).
Routing functionality
Routing functionality is required when multiple subnets are in
use. This functionality could be as simple as the current
"default route is up" model of IPv4 NAT, or it could involve
running an appropriate routing protocol.
The homenet routing environment may include traditional IP
networking where existing link-state or distance-vector protocols
may be used, but also new LLN or other "constrained" networks
where other protocols may be more appropriate. IPv6 VM solutions
may also add additional routing requirements. Current home
deployments use largely different mechanisms in sensor and basic
Internet connectivity networks. In general, LLN or other networks
should be able to attach and participate the same way or map/be
gatewayed to the main homenet.
It is desirable that the routing protocol has knowledge of the
homenet topology, which implies a link-state protocol may be
preferable. If so, it is also desirable that the announcements
and use of LSAs and RAs are appropriately coordinated.
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The routing environment should be self-configuring, as discussed
in the next subsection. An example of how OSPFv3 can be self-
configuring in a homenet is described in
[I-D.acee-ospf-ospfv3-autoconfig]. It is important that self-
configuration with "unintended" devices is avoided.
To support multihoming within a homenet, a routing protocol that
can make routing decisions based on source and destination
addresses is desirable, to avoid upstream ISP ingress filtering
problems. In general the routing protocol should support multiple
ISP uplinks and prefixes in concurrent use.
Self-Organisation
A home network architecture should be naturally self-organising
and self-configuring under different circumstances relating to the
connectivity status to the Internet, number of devices, and
physical topology.
The most important function in this respect is prefix delegation
and management. Delegation should be autonomous, and not assume a
flat or hierarchical model. From the homenet perspective, a
single prefix should be received on the border CPE from the
upstream ISP, via [RFC3363]. The ISP should only see that
aggregate, and not single /64 prefixes allocated within the
homenet.
Each link in the homenet should receive a prefix from within the
ISP-provided prefix. Delegation within the homenet should give
each link a prefix that is persistent across reboots, power
outages and similar short-term outages. Addition of a new routing
device should not affect existing persistent prefixes, but
persistence may not be expected in the face of significant
"replumbing" of the homenet. Persistence should not depend on
router boot order. Persistent prefixes may imply the need for
stable storage on routing devices, and also a method for a home
user to "reset" the stored prefix should a significant
reconfiguration be required.
The assignment mechanism should provide reasonable efficiency, so
that typical home network prefix allocation sizes can accommodate
all the necessary /64 allocations in most cases. For instance,
duplicate assignment of multiple /64s to the same network should
be avoided.
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Several proposals have been made for prefix delegation within a
homenet. One group of proposals is based on DHCPv6 PD, as
described in [I-D.baker-homenet-prefix-assignment],
[I-D.chakrabarti-homenet-prefix-alloc], [RFC3315] and [RFC3363].
The other uses OSPFv3, as described in
[I-D.arkko-homenet-prefix-assignment].
While the homenet should be self-organising, it should be possible
to manually adjust (override) the current configuration. The
network should also cope gracefully in the event of prefix
exhaustion.
The network elements will need to be integrated in a way that
takes account of the various lifetimes on timers that are used,
e.g. DHCPv6 PD, router, valid prefix and preferred prefix timers.
The homenet will have one or more borders, with external
connectivity providers and potentially parts of the internal
network (e.g. for policy-based reasons). It should be possible to
automatically perform border discovery at least for the ISP
borders. Such borders determine for example the scope of ULAs,
site scope multicast boundaries and where firewall policies may be
applied.
The network cannot be expected to be completely self-organising,
e.g. some security parameters are likely to need manual
configuration, e.g. WPA2 configuration for wireless access
control.
Fewest Topology Assumptions
There should be ideally no built-in assumptions about the topology
in home networks, as users are capable of connecting their devices
in ingenious ways. Thus arbitrary topologies will need to be
supported.
It is important not to introduce new IPv6 scenarios that would
break with IPv4+NAT, given dual-stack homenets will be commonplace
for some time. There may be IPv6-only topologies that work where
IPv4 is not used or required.
Naming and Service Discovery
The most natural way to think about naming and service discovery
within a home is to enable it to work across the entire residence,
disregarding technical borders such as subnets but respecting
policy borders such as those between visitor and internal
networks.
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This may imply support is required for IPv6 multicast across the
scope of the home network, and thus at least all routing devices
in the network.
Homenet naming systems will be required that work internally or
externally, though the domains used may be different in each case.
Proxy or Extend?
Related to the above, we believe that general existing discovery
protocols that are designed to only work within a subnet are
modified/extended to work across subnets, rather than defining
proxy capabilities for those functions.
We may need to do more analysis (a survey?) on which functions/
protocols assume subnet-only operation, in the context of existing
home networks. Some experience from enterprises may be relevant
here.
Adapt to ISP constraints
The home network may receive an arbitrary length IPv6 prefix from
its provider, e.g. /60 or /56. The offered prefix may be static
or dynamic. The home network needs to be adaptable to such ISP
policies, e.g. on constraints placed by the size of prefix offered
by the ISP. The ISP may use [I-D.ietf-dhc-pd-exclude] for
example.
The internal operation of the home network should not also depend
on the availability of the ISP network at any given time, other
than for connectivity to services or systems off the home network.
This implies the use of ULAs as supported in RFC6204. If used,
ULA addresses should be stable so that they can always be used
internally, independent of the link to the ISP.
It is expected that ISPs will deliver a static home prefix to
customers. However, it is possible, however unlikely, that an ISP
may need to restructure and in doing so renumber its customer
homenets. In such cases "flash" renumbering may be imposed. Thus
it's desirable that homenet protocols or operational processes
don't add unnecessary complexity for renumbering.
3.5. Summary of Homenet Architecture Recommendations
In this section we present a summary of the homenet architecture
recommendations that were discussed in more detail in the previous
sections.
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(Bullet points to be added in next version)
3.6. Implementing the Architecture on IPv6
The necessary mechanisms are largely already part of the IPv6
protocol set and common implementations, though there are some
exceptions. For automatic routing, it is expected that existing
routing protocols can be used as is. However, a new mechanism may be
needed in order to turn a selected protocol on by default. Support
for multiple exit routers and multi-homing would also require
extensions, even if focused on the problem of multi-addressed hosts
selecting the right source address to avoid falling foul of ingress
filtering on upstream ISP connections.
For name resolution and service discovery, extensions to existing
multicast-based name resolution protocols are needed to enable them
to work across subnets, within the scope of the home network.
The hardest problems in developing solutions for home networking IPv6
architectures include discovering the right borders where the domain
"home" ends and the service provider domain begins, deciding whether
some of necessary discovery mechanism extensions should affect only
the network infrastructure or also hosts, and the ability to turn on
routing, prefix delegation and other functions in a backwards
compatible manner.
4. References4.1. Normative References
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, December 1998.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3363] Bush, R., Durand, A., Fink, B., Gudmundsson, O., and T.
Hain, "Representing Internet Protocol version 6 (IPv6)
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